Processes and compositions for the reduction of nitrogen oxides in combustion effluents have been developed extensively over recent years. With the increased attention to the health risks and environmental damage caused by agents such as smog and acid rain, it is expected that NO.sub.x reduction research will continue to be pursued.
In the past, most processes for reducing nitrogen oxides levels in oxygen rich effluents have concentrated on achieving NO.sub.x reductions at temperatures below 2100.degree. F. and especially below 2000.degree. F. Most notable among these processes is that disclosed by Arand et al. in U.S. Pat. No. 4,208,386 which details the reduction of NO.sub.x in combustion effluents by introducing urea at temperatures between 1300.degree. F. and 2000.degree. F. The Arand et al. process has been significantly improved by disclosures such as U.S Pat. Nos. 4,751,065, 4,719,092, and 4,927,612, all to Bowers, U.S. Pat. No. 4,803,59 to Sullivan and Epperly, U.S. Pat. Nos. 4,844,878 to Epperly, Sullivan, and Sprague, 4,863,705 to Epperly, Sullivan, and Sprague, 4,873,066 to Epperly, Sullivan, and Sprague, 4,877,591 to Epperly and Sullivan, and 4,888,165 to Epperly and Sullivan. Each of these patents teaches the use of certain chemical "enhancers", useful themselves and which also shift the temperature range in which urea is most effective when they are used in conjunction with urea. Also disclosed are special techniques, such as cooling the effluent or highly diluting the treatment agent, which permit introduction at higher temperatures.
Other processes which improve upon the basic Arand et al. urea process are disclosed by U.S. Pat. Nos. 4,777,024 to Epperly, Peter-Hoblyn, Shulof, Jr., and Sullivan and 4,780,289 to Epperly, O`Leary, and Sullivan. These processes each involve introducing certain treatment agents using methods designed to maximize NO.sub.x reductions while minimizing the production or generation of other pollutants such as ammonia or carbon monoxide In other words, these patents teach processes which impact on the overall efficiency of the disclosed nitrogen oxides reducing processes. Although potentially effective at higher temperatures, these patents do not disclose particular treatment agents or conditions useful for the reduction of NO.sub.x at temperatures above 2100.degree. F.